A vane assembly for a gas turbine engine typically comprises a pair of guide vanes extending between a radially outer and a radially inner nozzle band assembly. In some prior art applications, the vane assembly is secured to inner and outer support members within a gas turbine engine. However, because the inner and outer support members can expand axially and radially to different extents and because the vane assembly may be formed of a different metal material than the support members and thus subject to a different degree of thermal expansion, contact between the vane assemblies and the inner and outer support members is sometimes broken allowing high pressure cooling air to leak out into the hot gas stream passing through the nozzle formed by the vane assemblies and resulting in a loss of efficiency of the engine. One prior art attempt to overcome the gas leakage problem caused by such differential thermal expansion has involved positioning of a vane assembly within a gas turbine engine such that the assembly is free to float between the inner and outer support members. The vane assembly includes a flange extending radially inward from the inner nozzle band which flange fits within a slot formed in the inner support member. The slot is wider in the axial direction than the flange so that the vane assembly is not only free to shift position radially but is also free to tilt about the flange in order to compensate for differential axial expansion of the inner and outer support members. In order to maintain a gas seal about this floating vane assembly, the vane assembly and the adjacent surfaces of the inner and outer support members are provided with chordically extending straight sealing edges against which the vane assembly is pressed by the pressure of the gas flow against the nozzle guide vanes.
It is believed that the above described floating vane assembly is susceptible to leaks around the straight sealing edges due to the lack of restraint on the vane assembly in its assembled position. More particularly, the vane assemblies are susceptible to distortion from heat differential between leading and trailing edges of the nozzle bands. For example, FIG. 1 is a radial view of a vane assembly having an outer nozzle band 2 and a pair of nozzle vanes 3. The leading edge 4 of band 2 receives gas at a typical temperature of about 1400.degree. F. while the gas temperature at trailing edge 5 may be about 1800.degree. F. This 400.degree. F. temperature differential causes the nozzle band 2 to distort or bow as indicated by dashed lines 6. Support for the vane assembly is reduced to a contact area at 7 thus allowing the assembly to rock about contact area 7. Such rocking creates steps between adjacent nozzle bands and between the nozzle band and adjacent supporting members. Gas leakage through such steps detrimentally affects engine performance. More particularly, since the vane assemblies are not restrained radially and circumferentially, the forces exerted on the vane assembly that determine the position of the vane assembly are not statically determinant. Accordingly, gas leakage may occur around these floating vane assemblies.